Abrasive articles are used in any of a variety of fields for abrading material from a surface of a workpiece. For example, an abrasive disc may be releasably mounted on a back-up pad for rotative movement by a random orbital sander. When the disc is rotated, and the exposed abrasive surface of the disc is urged against the workpiece surface, material may be removed from the workpiece. This operation may be desirable for surface refinement purposes, or for the removal of excess material from the workpiece.
Abrasive discs are typically releasably attached to a back-up pad, which supports the abrasive disc during the abrading process. The back-up pad includes a generally planar major surface, to which the abrasive article, such as a disc or sheet, may be attached. Although back-up pads may be hand held, back-up pads are more commonly used in conjunction with powered abrading apparatuses, such as electric or pneumatic sanders.
Several types of abrasive discs have some type of attachment system incorporated into the disc to enable the disc to be releasably attached to a back-up pad, e.g., discs backed with pressure sensitive adhesive, textile materials, or engagement elements.
Textile backed discs typically include a textile loop material on the back surface of the abrasive article opposite the abrasive surface. The textile material can be, for example, woven or non-woven web, brushed nylon, brushed polyester, knitted fabrics, and stitch-bonded fabrics. Textile discs are described in U.S. Pat. No. 4,437,269 (Shaw) and U.S. Pat. No. 4,609,581 (Ott), and an example of a textile abrasive disc is available from the Minnesota Mining and Manufacturing Company of St. Paul, Minn. under the designation Hookit.TM. discs. Textile discs are typically used in conjunction with a back-up pad having a plurality of engaging members that are bonded to the attachment surface of the back-up pad. The engaging members on the back-up pad are designed to engage the textile material of the textile disc, to secure the abrasive disc to the back-up pad.
U.S. Pat. No. 4,437,269 (Shaw) relates primarily to textile discs of the type described above, but also briefly discusses a type of disc referred to herein as the "stalk" disc. Specifically, the '269 patent discloses a back-up pad and a disc, wherein one of the two components has a textile material on one face, and the other of the pad and the back of the disc has a layer thereon from which extend loop-engaging or curl-engaging members in the form of mono-filament stalks having unhooked ends. The stalks are engaging elements which project from a backing, and slidingly intermesh with, but do not hook, a loop-like textile material on an opposed surface to attach the two surfaces together.
U.S. Pat. No. 5,672,186 describes an abrasive article for releasable affixation to a mating surface having engaging structures which includes a plurality of hooking stems affixed to and projecting from the engagement surface of the article. The hooking stems each include means for hooking the engaging structures of the mating surface to releasably affix the abrasive article to the mating surface. In one variation, the abrasive layer is bonded directly to the surface of the substrate opposite the engagement surface.
The abrasive articles of the '186 patent typically are made by depositing molten thermoplastic polymeric material onto a smooth surface which bears a plurality of cavities which form the engaging elements or their precursors to provide a flat sheet-like substrate. The substrate is then removed from the surface on which it is formed, any precursor engaging elements converted to engaging elements, and an abrasive coating is applied to the surface opposite that which bears the engaging elements. Such application typically involves coating this surface with a liquid curable binder composition, depositing abrasive particles on the coated surface so that they are at least partially embedded in the exposed surface of the coating, at least partially curing the coating by heating, applying a second coating of a second binder material over the exposed surface and deposited abrasive particles and then curing any uncured first binder coating and the second binder coating by further heating to provide the abrasive article.
Unfortunately, the thermoplastic polymeric material from which the substrate is formed typically increases in dimension on heating to a greater degree than that of the materials that are typically used as binder materials to make the abrasive coating. Such a differential in dimensional expansion typically causes the substrate to distort as a result of heat used to cure the binder material of the abrasive layer and may cause undesirable curling or other deformation in the resultant abrasive product.
It is, thus, desirable to provide an abrasive disc which overcomes the disadvantage of being distorted on formation due to the differential dimensional expansion on heating of the thermoplastic polymer and the binder material.